Phase-change random access memory (PCRAM) devices, which are known in the art, employ storage cells that are each typically formed by a layer of phase-change, or chalcogenide material, for example, a Ge2Sb2Te5 alloy (GST). Each phase-change material (PCM) storage cell may be programmed between crystalline and amorphous structural states, wherein an electrical resistivity of the cell is significantly higher when the PCM is in the amorphous state than when the PCM is in the crystalline state. Each programmed cell may be read by biasing the cell and sensing the current passing therethrough. Programming, or writing to each PCM storage cell is typically accomplished by applying an appropriate current pulse through each cell, for example, a pulse having a relatively high amplitude and relatively short duration, to change the PCM to the amorphous state (RESET), or a pulse having a medium amplitude and a relatively long duration, to switch the PCM to the crystalline state (SET). (The RESET state may be logical ‘0’, while the SET state a logical ‘1’.) Each PCM is typically sandwiched between an upper contact and a lower resistive electrode, such that the current pulses being driven through each PCM storage cell induces the phase transition, via heat generation, close to the interface with the resistive electrode, or heater.
In order to increase programming efficiency, a contact area between the PCM and the resistive electrode/heater is typically made as small as practicable, thereby increasing the current density, for a given current required to set and reset the PCM storage cell. In order to increase programming endurance, attention has been paid to the quality of the interface between the PCM and the resistive electrode/heater, for example, in order to reduce separation at the interface and to prevent significant interfacial diffusion from the electrode into the PCM. However, there is still a need for new memory device structures, which can effectively increase the programming endurance and/or efficiency of the PCM storage cells thereof; such structures are described in the present disclosure.